Fix license system - tier-aware key generation and activation

- generateLicenseKey() now accepts tier parameter and prefixes keys:
  T=Trial, B=Basic, P=Professional, E=Enterprise
- Added detectLicenseTier() to extract tier from key prefix
- Updated isValidLicenseFormat() regex to accept tier prefixes
- Simplified activateLicense() to use detectLicenseTier()
- Added license_generate API endpoint for generating sample keys
- Added "Generate Sample License Key" UI section with tier selector
- Added copy/use buttons for generated keys

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

webapp/api.php

@@ -289,6 +289,10 @@ try {
             handleLicenseUsage($db);
             break;
 
+        case 'license_generate':
+            handleLicenseGenerate($db);
+            break;
+
         default:
             jsonResponse(['error' => 'Invalid action'], 400);
     }
@@ -3717,6 +3721,49 @@ function handleLicenseUsage($db) {
     ]);
 }
 
+/**
+ * Generate sample license keys (admin only, for testing)
+ */
+function handleLicenseGenerate($db) {
+    require_once __DIR__ . '/includes/auth.php';
+
+    if (!isAdmin()) {
+        jsonResponse(['error' => 'Admin access required'], 403);
+        return;
+    }
+
+    if ($_SERVER['REQUEST_METHOD'] !== 'GET') {
+        jsonResponse(['error' => 'GET method required'], 405);
+        return;
+    }
+
+    $tier = $_GET['tier'] ?? 'trial';
+
+    // Map tier name to constant
+    $tierMap = [
+        'trial' => LICENSE_TRIAL,
+        'basic' => LICENSE_BASIC,
+        'professional' => LICENSE_PROFESSIONAL,
+        'enterprise' => LICENSE_ENTERPRISE
+    ];
+
+    $tierConst = $tierMap[$tier] ?? LICENSE_TRIAL;
+    $key = generateLicenseKey($tierConst);
+
+    global $LICENSE_LIMITS;
+    $limits = $LICENSE_LIMITS[$tierConst];
+
+    jsonResponse([
+        'success' => true,
+        'license_key' => $key,
+        'tier' => $tier,
+        'tier_name' => $limits['name'],
+        'max_entries' => $limits['max_entries'],
+        'max_users' => $limits['max_users'],
+        'features' => $limits['features']
+    ]);
+}
+
 /**
  * Export full database backup as JSON
  */